This invention relates to hybrid electric vehicles, and more particularly to such vehicles using an internal combustion engine which receives combustion air under pressure.
Enhancement of the operation of internal combustion engines by the use of superchargers has been known for almost a century. In general, a supercharger is an air pump which is driven by the engine, and which compresses the air provided to the air intake port of the engine. The air pump of a supercharger is often described as being xe2x80x9cpositive-displacement,xe2x80x9d to thereby indicate that a fixed volume of air is move during each rotation of the compressor shaft. Compression of the air provided to the intake manifold allows a greater mass of air to be forced into each cylinder during the intake portion of the operating cycle, which in turn allows combustion of a greater mass of fuel during each cycle of operation. This improves the xe2x80x9cvolumetric efficiencyxe2x80x9d or the amount of power which can be produced by each increment of displaced volume. More power can be produced by an engine operating with a supercharger than by a corresponding engine lacking a supercharger.
It was discovered that supercharging an engine did indeed increase the output power or torque, but it also increased the stresses on engine parts, which tended to contribute to a lesser reliability. The power gains achieved by a supercharger tended to be less than expected, because of the shaft power consumed by the air compressor itself. A concomitant of the use of a supercharger to improve the volumetric efficiency an increase in the fuel consumption per displaced volume, because the ratio of fuel to air remains relatively constant for proper combustion. In general, it was found to be more practical to achieve increased power by a conventionally aspirated engine of larger displacement than by a supercharged engine.
Turbocharging was devised as a method for achieving some of the gains of supercharging, without attendant disadvantages. A turbocharger is an air compressor, generally centrifugal, which is driven by a turbine associated with the exhaust of the internal combustion engine. The exhaust gases drive the turbine, which spins the centrifugal compressor, and the resulting compressed air is provided to the air intake port of the engine to provide improved volumetric efficiency.
As with superchargers, turbochargers were found to be less than perfect. Early turbocharged vehicles suffered from carbonization of lubricating oil in the turbine due to the heat of the exhaust gases driving the turbine, and this effect was found to be most egregious when the engine was turned off, as the oil xe2x80x9cbakedxe2x80x9d in place, as oil flow stopped concurrently with turning off of the engine. It had initially been anticipated that the energy for driving the turbocharger was xe2x80x9cfreexe2x80x9d in that the drive energy would otherwise be wasted; the effect of the presence of the turbine in the exhaust system of the engine tended to increase the back pressure, which tended to offset the improvement in volumetric efficiency provided by the positive pressure at the air intake port. Another disadvantage of the turbocharger is that of xe2x80x9clag,xe2x80x9d which refers to reduction of the boost air pressure, during acceleration, relative to what might be expected at a corresponding static engine speed. In other words, the turbine speed lagged the engine speed, due to inertia or possibly other factors. Consequently, the boost air pressure during acceleration, when extra power or torque is needed, was small, while the boost air pressure during cruise was large, but generally unnecessary. These disadvantages resulted in little use of turbochargers in gasoline-powered automobiles.
Since the early 1970s, there has been an emphasis on vehicle fuel mileage. The Government has promulgated fleet mileage requirements in an attempt to reduce overall fuel consumption. In response to the perceived need for improved mileage, automobiles have been made lighter, and engine displacements have been reduced. The reduction in shaft power per operating cycle occasioned by the reduced displacements has been partially overcome by increasing the engine operating speeds. These changes, coupled with modern electronic control systems, has been effective in maintaining perceived automobile performance, while improving fuel mileage.
In an effort to further improve mileage, automotive manufacturers have been experimenting with nonstandard propulsion systems. One proposed vehicle drive system is powered by a tank of compressed air, but this arrangement lacks range, and is not readily xe2x80x9crefueledxe2x80x9d as its compressed-air tanks require pressures which may exceed those readily available at gas stations. Battery-powered electrically-driven vehicles are available, but are widely recognized as having insufficient range for ordinary use. Improvements in battery technology may one day make such battery-operated vehicles practical. However, the need to recharge the batteries with substantial amounts of energy means that technological and infrastructure changes may be required to provide fast charging at convenient xe2x80x9celectricxe2x80x9d recharge stations.
A fuel-consuming hybrid electric vehicle has come to be considered more practical than a pure-electric vehicle because of its ability to use conventional liquid-fuel infrastructure, because of its relatively great range, attributable to the relatively high energy density of liquid fuels. The environmental objections to such vehicles appear to be decreasing, as the effects of operation of coal-fired and other electrical generating plants on the environment, attributable to the need to produce the energy to recharge electric vehicles, becomes widely known.
Improved vehicles are desired.
A hybrid electric vehicle according to an aspect of the invention includes an internal combustion engine which receives fuel, mixes the fuel with air from an air intake port to thereby form a fuel-air mixture, and combusts the fuel-air mixture to rotate a drive shaft. The vehicle also includes an electrically operated traction motor for driving the vehicle. An electrical generator is mechanically coupled to the drive shaft of the engine, for being driven by its rotation. Rotation of the generator, in turn, generates electrical power for use by the traction motor. The traction motor may receive the electrical power directly from the generator, but a preferred arrangement converts alternating current from the generator into direct voltage, which is stored in a traction battery, used by the traction motor, or both. The generator includes a cooling air input port, to which pressurized air is provided for cooling the generator. An air mover is pneumatically coupled to air intake port of the engine and to the cooling air input port of the generator, for creating a positive air pressure, and for coupling the positive air pressure to the air intake port and to the cooling air input port. In a preferred embodiment of the invention, the air mover is mechanically driven from the generator shaft, or ultimately from the drive shaft of the engine by way of any intermediary mechanical arrangement. In another embodiment, the air mover is driven by an auxiliary electrical motor, which is preferably powered from a battery which is recharged by the generator. In one embodiment, the internal combustion engine is a diesel engine.
A method, according to another aspect of the invention, is for operating a hybrid electric vehicle. The method includes the step of rotating a drive shaft of an internal combustion engine by combusting fuel with air from an air intake port. The shaft of an electrical generator is rotated in response to rotation of the drive shaft, for thereby generating electrical power. The traction motor is operated from time to time using electrical power, to drive, or to aid in driving, the vehicle. An air mover or compressor is operated in order to produce compressed air. The compressed air is routed from the air mover to a cooling air input port of the generator and to the air intake port of the engine. According to a preferred mode of the method of the invention, the step of driving the air mover includes the step of coupling mechanical rotation of the drive shaft to a drive shaft of the air mover. This step may include the step of driving an intermediary device, which is preferably the generator shaft. In an alternative mode of the method, the step of driving the air mover includes the step of applying electrical energy to an auxiliary electrical motor mechanically coupled to the air mover. This auxiliary electrical motor may be driven from a battery which is recharged by the generator.